The present invention relates to a semiconductor integrated circuit (i.e., a semiconductor device) testable by a test system even when the semiconductor integrated circuit operates faster than the test system.
A test technique, called dynamic burn-in testing, for accelerating the aging of semiconductor devices has been known in the art. The purpose of a dynamic burn-in test operation is to remove or screen out devices that are subject to time and stress-dependent failures. More specifically, such a screening-out operation is carried out by applying a supply voltage in excess of the rated voltage to a test-target device at constant temperature while applying to the device an input signal similar to one that is applied in the normal operation. A monitored burn-in system has, in addition to a dynamic burn-in function, a device output monitoring/observing function.
With the speed-up of the operation of semiconductor devices, their maximum operation frequency has increased. Japanese Unexamined Laid-Open Patent Application Publication No. 6-187797 discloses a technique. In accordance with the 6-187797 technique, in order to enable a slow test system to perform testing of a fast memory device, the frequency of an external clock signal is increased in the inside of the memory device for generating an address signal in synchronization with an internal clock signal having the increased frequency. However, the 6-187797 technique makes no disclosure of the monitoring of device output.
In accordance with the monitored burn-in system described above, the monitoring of the output of the device is repeatedly carried out at given time intervals. However, during the device output monitoring, there occurs a drop in voltage stress because the supply voltage of the device is lowered down to the rated voltage. Accordingly, there has been strong demand for reductions in the time required for each monitoring operation. To satisfy such demand, the devices are required to operate at a high speed as required in their normal operation if they are capable of high-speed operation, even during the device output monitoring under burn-in testing. However, because of the various limits of test systems, the devices, although they have the capability of operating at a high speed, are practically forced to operate at a lower speed during the device output monitoring under burn-in testing.
The operation of monitoring device outputs is indispensable also to functional testing of high-speed devices. However, such a device output monitoring operation has been beyond the capability of a low-speed test system.